Thermoeconomic performance and optimization of a novel cogeneration system using carbon dioxide as working fluid

Highlights: • A new cogeneration system with carbon dioxide as working fluid is proposed and analyzed. • Parametric studies are performed to identify the main decision parameters. • Thermodynamic and economic optimizations are performed for the system. • The cogeneration system can be changed to a refrigeration system. - Abstract: A novel cogeneration power and refrigeration system using carbon dioxide as working fluid, is proposed, analyzed and optimized. The system is an internally interacting combination of a supercritical carbon dioxide recompression Brayton cycle and a transcritical carbon dioxide refrigeration cycle with an expander. The system proves to perform either as a cogeneration system producing power and refrigeration or only refrigeration system. The effects on system's thermodynamic and economic performances are quantified of the main decision parameters. The systems performance is optimized for having either maximum first law efficiency or maximum second law efficiency or minimum total product unit cost, for both the cogeneration and refrigeration only situations. It is shown that, for the cogeneration situation, the minimum total product unit cost in cost optimal design case is 3.5% lower than that for the exergy efficiency optimal design cases. For the refrigeration only situation, it is observe that the minimum total product unit cost obtained for the cost optimal design case is 18.9% and 4.2% lower than those for the thermal and exergy efficiencies optimal design cases, respectively. The highest value of refrigeration capacity is obtained for the thermal optimal design case for the system when it produces refrigeration only. At the refrigeration only situation the lowest evaporator temperature is achieved when the system is optimized for maximum exergy efficiency.